Semiconductor manufacturing method and apparatus

ABSTRACT

The present invention aims to provide processes and equipments for manufacturing semiconductors, according to which oxidation of wafer surfaces can be controlled by simple means and contaminants promoting oxidation and contaminants inviting a decreased yield of wafers can also be totally controlled. To achieve the object above, the present invention provides a process for manufacturing a semiconductor, characterized in that a substrate is treated while exposing the surface of the substrate with a negative ion-enriched gas; and an equipment for manufacturing a semiconductor comprising a gas channel through which a gas to be treated is passed; a negative ion-enriched gas generator consisting of a gas cleaner located at an upstream part of said gas channel and a negative ion generator located at a downstream part thereof: and means for supplying the resulting negative ion-enriched gas to the surface of each substrate.

TECHNICAL FIELD

The present invention relates the manufacture of semiconductors,particularly processes and equipments for manufacturing semiconductorsin leading-edge industries such as semiconductors and liquid crystals.

BACKGROUND ART

Air cleaning in the working environment Is very important for themanufacture of semiconductors, which normally takes place in anair-conditioned space called clean room. A conventional air cleaningtechnique in a semiconductor factory (clean room) is explained withreference to FIG. 8.

In FIG. 8, ambient air 1 first passes through a prefilter 2 where coarseparticles are eliminated and then the temperature and humidity areconditioned in an air conditioner 3 and then dusts are collected by amedium-performance filter 4. Then, fine particles are collected by anHEPA filter 6 at the ceiling of a clean room 5. Such an air cleaningsystem maintains a microparticle concentration of class 10,000 inthe-clean room. In FIG. 8, references 7-1 and 7-2 represent fans andarrows indicate air streams.

The air cleaning system in conventional clean rooms for the purpose ofremoving microparticles is designed as shown in FIG. 8 and effective forremoving microparticles but not effective for removing gaseous hazardouscomponents.

As improvements in the quality and precision of products increasinglyadvance in the recent semiconductor industry, not only microparticles(particulate substances) but also gaseous substances have come toparticipate in contamination of semiconductors.

However, conventional dust filters for clean rooms (e.g., HEPA filters,ULPA filters, etc.) as shown in FIG. 8 can collect only microparticles,but gaseous hazardous components from ambient air are not collected andbut introduced into clean rooms. Such gaseous hazardous componentsinclude e.g. gases called hydrocarbons (HCs) derived from automobileemissions and outgassing (gas release) from polymer resin productswidely used as consumer products; and basic (alkaline) gases such as NH₃and amine.

Among them, hydrocarbons (HCs) must be completely eliminated becausethey cause pollution even at very low concentrations as gaseoushazardous components in normal air (indoor and outdoor air). Recently,outgassing from the materials of clean rooms or polymer resins ofmanufacturing equipments or appliances used has become a problem as asource of hydrocarbons (HCs).

These gaseous substances in question also include those generated duringoperations in clean rooms. That is, typical clean rooms contain gaseoussubstances not only introduced from ambient air (those having passedthrough microparticle-collecting filters for clean rooms to enter theclean rooms) but also generated in the clean rooms so that they containhigher concentrations of gaseous substances than ambient air, whichincrease the possibility of contaminating semiconductor substrates.

When microparticulate contaminants are deposited on the surfaces ofsemiconductor substrates, they cause breakage or short in circuits(patterns) on the substrate surfaces, resulting in failure. When gaseoushazardous components, especially hydrocarbons (HCs) are deposited on thesurfaces of semiconductor substrates, they increase the contact angle toadversely affect e.g. substrate-resist affinity (compatibility). Thelowered substrate-resist affinity adversely affects the film thicknessof the resist or adhesion of the resist to the substrate. Hydrocarbons(HCs) also have the disadvantage that they deteriorate the pressureresistance of oxide films on the surfaces of semiconductor substrates(lowered reliability). The contact angle here means the contact angle ofwetting with water and indicates the degree of contamination onsubstrate surfaces. That is, substrate surfaces stained with hydrophilic(oily) contaminants repel water and resist wetting. This increases thecontact angle between the substrate surfaces and water drops. Thus,contamination is more serious at larger contact angles, whilecontamination is weaker at smaller contact angles. NH₃ causes productionof ammonium salts or the like to invite haze (resolution failure) insemiconductor substrates.

For these reasons, the productivity (yield) of semiconductor products Islowered by not only microparticles but also gaseous contaminants asdescribed above.

Especially, the above gaseous substances as gaseous hazardous componentsare generated from the sources described above and more concentrated inclean rooms than ambient air so that they are deposited on substrates tocontaminate their surfaces because air circulation is recently increasedin clean rooms for saving energy.

To address these contamination problems, we have previously proposedvarious space cleaning methods using photoelectrons or photocatalysts.

For example, methods for removing microparticulate substances usingphotoelectrons are described in JP-B-HEI-3-5859, JP-B-HEI-6-74909,JP-B-HEI-8-211 and JP-B-HEI-7-121367. Methods for removing gaseoushazardous components using photocatalysts are described in JapanesePatent No. 2863419 and Japanese Patent No. 2991963. A method forremoving microparticles and gaseous substances at the same time bycombining photoelectrons and photocatalysts is described in JapanesePatent No. 2623290.

It is thought that current Al wirings will not suffice for patterns onwafer surfaces of semiconductor products with higher quality(microfabricated products) in future and will be replaced by Cu wirings.Thus, it will be necessary in future to use Cu wirings and interlayerdielectrics with low dielectric constant (low-k) to shorten the delaybecause the combination of current Al wirings and SiO₂ dielectricsrequires a long wiring delay under compact wiring-and design rules forfuture ultra large scale Integrated circuits (ULSIs). However, Cumaterials are more susceptible to oxidation than conventional Al or W.Thus, it will be also important in future to controls gaseoussubstances, especially those oxidizing wafer surfaces (wiring surfacesand interfaces) though it was sufficient in the past to pay attention toremoval of only microparticles in semiconductor manufacturingenvironments.

Possible materials promoting oxidation of wafer surfaces include water(moisture) and organic matters (HCs) in clean room air, but it isdifficult to control moisture present at about 45-50% (RH) in clean roomair. This is because excessive reduction of moisture in the airadversely affects the health of operators working in the clean room.

Thus, it would be desirable to provide a novel method for controlling(inhibiting) oxidation of wafer surfaces by controlling materials inclean rooms including moisture and HCs.

In view of the circumstances described above, the present invention aimsto provide processes and equipments for manufacturing semiconductors,according to which oxidation of wafer surfaces can be controlled bysimple means and contaminants promoting oxidation and contaminantsinviting a decreased yield of wafers can also be totally controlled.

DISCLOSURE OF THE INVENTION

To solve the problems described above, the present invention providesprocesses for manufacturing semiconductors, characterized in thatsemiconductor substrates are treated while using a negative ion-enrichedgas obtained by a negative ion generator to inhibit oxidation of thesurfaces of the substrate during semiconductor manufacturing steps.

Accordingly, an embodiment of the present invention relates to a processfor manufacturing a semiconductor, characterized in that a substrate istreated while exposing the surface of the substrate with a negativeion-enriched gas. In the present invention, the negative ion-enrichedgas is preferably prepared by passing a clean gas preliminarily freed ofmicroparticles and/or chemical contaminants through a negative iongenerator. The chemical contaminants here include one or more selectedfrom the group consisting of ionic components. Inorganic matters andorganic matters. In the present invention, the negative ion-enriched gasis preferably prepared by passing a gas having a microparticleconcentration of class 100 or less, an ionic component concentration of10 μg/m³ or less and an organic matter concentration of 10 μg/m³ or lessthrough a negative ion generator.

Another embodiment of the present invention provides an equipment formanufacturing a semiconductor comprising a gas channel through which agas to be treated is passed; a negative ion-enriched gas generatorconsisting of a gas cleaner located at an upstream part of said gaschannel and a negative ion generator located at a downstream partthereof; and means for supplying the resulting negative ion-enriched gasto the surface of each substrate.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a flow chart showing specific processing steps on asemiconductor substrate in a semiconductor factory (clean room).

FIG. 2 is a schematic view showing an example of an apparatus forobtaining a negative ion-enriched gas used In the present invention.

FIG. 3 is a schematic view showing another example of an apparatus forobtaining a negative ion-enriched gas used in the present invention.

FIG. 4 is a schematic view showing another example of an apparatus forobtaining a negative ion-enriched gas used in the present invention.

FIG. 5 is a schematic view showing another example of an apparatus forobtaining a negative ion-enriched gas used in the present invention.

FIG. 6 is a schematic view showing another example of an apparatus forobtaining a negative ion-enriched gas used in the present invention.

FIG. 7 is a schematic view showing another example of an apparatus forobtaining a negative ion-enriched gas used in the present invention.

FIG. 8 is a schematic view showing an air cleaning system commonly usedin conventional semiconductor factories (clean rooms).

THE MOST PREFERRED EMBODIMENTS OF THE INVENTION

The present invention was accomplished on the basis of the finding thatsemiconductor products suitable for the needs for high performance canbe prepared by treating substrates while exposing them to a gas having ahigh level of cleanliness (i.e. very low microparticle concentration andchemical contaminant concentration) and rich in negative ions (i.e.negative ion-enriched gas) to inhibit oxidation of the substrates duringvarious substrate processing steps at a given stage of semiconductormanufacturing processes in a clean room and thereby improve the yield ofthe semiconductor products.

The method for preparing a negative Ion-enriched gas used in theprocesses of the present invention is divided into a negative iongenerating stage and a gas cleaning stage before generating negativeions. Each stage is explained below.

A. Negative Ion Generating Methods

Our studies showed that oxidation of substrate surfaces is inhibited byexposing substrates to a negative ion-enriched gas. The “negative ion”(also called as “minus ion”) here refers to a substance formed byattaching n electron to an electrophilic substance such as oxygen, e.g.small ions (hydrate ions) such as O₂ ⁻(H₂O)_(n) formed by attaching oneor more water molecules to a negatively charged oxygen molecule. Ionshaving CO_(x) ⁻ or NO_(x) ⁻ as a core such as CO₃ ⁻(H₂O)_(n) and NO₂⁻(H₂O)_(n) can also be taken as “negative ions” according to the presentinvention. The concentration of negative ions sufficient for inhibitingoxidation of substrate surfaces varies with the purpose/type of thesemiconductor, the desired performance for the semiconductor, coexistingmaterials and other factors, but normally 1,000 negative ions/mL ormore, preferably 5,000 negative ions/mL or more, more preferably 10,000negative ions/mL or more, still more preferably 50,000 negative ions/mLor more. Preferred negative ion concentrations can be determined byappropriate pretests depending on the purpose/type of the semiconductor,the desired performance, coexisting materials and other factors. Thereason why oxidation of substrate surfaces is inhibited by negativeion-enriched gases has not been unknown well, but it is supposed thatnegative ions have a reducing effect on the surfaces of substrates.

The concentration of negative ions in a gas can be determined bymeasuring the electrical mobility of the ions under electric field. Suchinstruments for measuring the concentration of negative ions in a gasare commercially available e.g. under trade name Air Ion Counter Model83-1001B from Dan Science.

Means for generating negative ions include methods using photoelectronsas proposed by us (JP-B-HEI-8-10616, Japanese Patent No. 3139591),discharge, water spray, irradiation, etc. Various methods for generatingnegative ions are explained below.

A-1: Negative Ion Generating Method Using Photoelectrons

The negative ion generating method using photoelectrons involvesirradiating a photoelectron emitting member with UV rays from a UVsource such as a UV lamp optionally in the presence of an electric fieldto generate photoelectrons, thereby forming negative ions. Here, anelectric field can be formed by placing an electrode (positiveelectrode) on the side opposite to the photoelectron emitting member(negative electrode) to accelerate photoelectron emission from thephotoelectron emitting member. Thus, negative ion generators usingphotoelectrons comprise a photoelectron emitting member and a UV sourcesuch as a UV lamp, and optionally an electrode for establishing anelectric field. Inert gases such as N₂ can also be used as feed gasesother than air.

The photoelectron emitting member is not limited so far as it can emitphotoelectrons upon UV irradiation and preferably has a smallerphotoelectric work function. From the viewpoint of the effect andeconomical efficiency, the member is preferably any one of Ba, Sr, Ca,Y, Gd, La, Ce, Nd, Th, Pr, Be, Zr, Fe, Ni, Zn, Cu, Ag, Pt, Cd, Pb, Al,C, Mg, Au, In, Bi, Nb, Si, Ti, Ta, U, B, Eu, Sn, P and W or compounds oralloys or mixtures thereof. These can be used alone or in combination oftwo or more. Suitable composite materials include physically compositematerials such as amalgam.

Compounds of the elements above include oxides such as BaO, SrO, CaO,Y₂O₃, Gd₂O₃, Nd₂O₃, ThO₂, ZrO₂, Fe₂O₃, ZnO, CuO, Ag₂O, La₂O₃, PtO, PbO,Al₂O₃, MgO, In₂O₃, BiO, NbO and BeO; borides such as YB₆, GdB₆, LaB₅,CeB₆, EuB₆, PrB₆ and ZrB₂; and carbides such as UC, ZrC, TaC, TiC, NbCand WC. Suitable alloys of the elements above include brass, bronze,phosphor bronze, Ag—Mg alloys (Mg=2-20 wt %), Cu—Be alloys (Be=1-10 wt%) and Ba—Al alloys, among which Ag—Mg alloys, Cu—Be alloys and Ba—Alalloys can be preferably used. Oxides of the elements above can beobtained by heating only the surface of a metal in the air or chemicallyoxidizing it. Alternatively, a metal or alloy material of any one of theelements above can be heated before use to form an oxide layer withprolonged stability on its surface and this oxide layer can be used as aphotoelectron emitting member. For example, an Mg—Ag alloy can betreated at a temperature of 300-400° C. in water vapor to form an oxidefilm on its surface, and such an oxide film can be used as aphotoelectron emitting member over a long period because it hasprolonged stability.

Photoelectron emitting materials can be used in combination with othermaterials. As an example, a UV transparent material such as glass can becombined with a material capable of emitting photoelectrons(JP-B-HEI-7-93098, JP-A-HEI-4-243540).

The photoelectron emitting member can also be incorporated into aphotocatalyst such as TiO₂ (JP-A-HEI-9-294919). This form is preferredfor some types of equipments or desired performances because thephotocatalyst can eliminate any substance adversely affecting thephotoelectron emitting member to stabilize It over a long period whilecoexisting gaseous contaminants can also be eliminated.

The shape of the photoelectron emitting member can be appropriatelyselected from plates, pleated sheets, grids and others depending on thepermeation mode of the negative ion generating gas or the type of theequipments. Among them, grid-type photoelectron emitting members arepreferred for some types of equipments applied because negative ions canbe generated without forming an electric field when a gas is passed fromthe bottom to the top of the photoelectron emitting member. Thephotoelectron emitting member can be preferably incorporated into theirradiation source described below for some types of equipments appliedbecause the size of the photoelectron emitter is reduced. This can beaccomplished by e.g. affixing a photoelectron emitting member to thesurface of a UV lamp.

The irradiation source for emitting photoelectrons from thephotoelectron emitting member is not limited so far as it irradiates thephotoelectron emitting member to emit photoelectrons, but normally UVrays or radiation are preferred (Japanese Patent No. 2623290,JP-B-HEI-6-74910), and UV rays are especially preferred because they canbe used simply and safely.

The type of the UV source that can be used is not limited so far as itirradiates the photoelectron emitting member to emit photoelectrons,preferably a mercury lamp such as a germicidal lamp in terms of sizereduction.

The optional electric field under which photoelectrons are emitted ispreferably 0.1 V/cm to 1 kV/cm, and can be appropriately determined bypretests depending on the configuration and structure of the equipments.The electrode member used for forming the electric field is not limitedso far as it produces no impurities and allows the photoelectronemitting member to effectively emit photoelectrons, and it may be in theform of a line, bar, grid or plate made from SUS, Cn—Zn or W. Theseelectrode members are placed to create an electric field near thephotoelectron emitting member so that photoelectrons can be emittedunder the electric field.

A-2: Negative Ion Generating Method Using Discharge

The discharge-based method involves emitting electrons by a discharge ina gas to generate negative ions using an apparatus comprising adischarge electrode and a counter electrode.

Suitable discharges for generating negative Ions include thosewell-known in the art such as corona, glow, arc, spark, surfacecreepage, pulse, high-frequency, laser, trigger and plasma discharges.Among them, surface creepage and pulse discharges are preferred for somepurposes in terms of the size reduction of the equipments because ofhigh concentrations of negative ions generated. Corona discharge ispreferred in terms of simplicity, operability and effect.

A-3: Negative Ion Generating Method Using Water Spray

The negative ion generating method using water spray involves generatingnegative ions via Lenard effect by atomizing water, e.g. negative ionscan be generated by spray charging of droplets when water is atomized inthe air. The mechanism by which negative ions are generated via Lenardeffect can be supposed as follows. Water molecules are polar moleculeshaving electrically positive and negative charges and their positivesides are outwardly oriented on the water surface (oriented dipoles).These oriented dipoles attract many negative ions to form an electricbilayer, which produces a negatively charged air when an energy such asa high pressure is applied. That is, when water is atomized under highpressure, negatively ionized air is produced because the water surfaceis positive and the adjacent air becomes negative. Then, this air isvaporized to remove coexisting excess water if desired, whereby anegative ion-enriched air is formed.

A-4: Negative Ion Generating Method Using Irradiation

The irradiation-based method involves exposing air to a radiation togenerate negative ions. Radiations that can be used in this method arenot limited so far as they generate ions from radiation sources, such asX-rays, α-rays, γ-rays and β-rays. Among them, X-rays, α-rays and γ-raysare preferred in terms of operability or the like, with X-rays beingespecially preferred. X-ray irradiation uses ions obtained by exposinggas molecules to X-rays, and normally gas molecules are bombarded withX-rays obtained by irradiating a metal target with accelerated electronbeams to ionize air molecules.

The mechanism of the ionization by soft X-rays that are especiallypreferred for use in the processes of the present invention is explainedas follows. Air molecules absorb irradiating X-rays or photons(wavelength 0.2-0.3 nm) to become ionized or photoionized. Ionizedelectrons collide with neutral electrons and molecules to ionize thembecause of their high kinetic energy. These ionizations continuouslyoccur by electron avalanche to generate large amounts of ions. The ionsgenerated here include both positive and negative ions, of which onlypositive ions are removed by suitable well-known means such as anelectrode plate to give a gas enriched in only negative ions.

The photon energy of soft X-rays preferred for use in the present methodis several KeVs to 10 KeV or less. i.e. about {fraction (1/10)} times orless of the energy of hard X-rays used for radiography, but a shield isrequired if irradiation takes place in a region which operators mayenter. The shield can be e.g. a metal plate having a thickness of about1 mm or a plastic (e.g. vinyl chloride) plate having a thickness ofabout 2-3 mm.

A gas enriched in only negative ions can also be obtained by the sameprocedure as described above using α-rays or γ-rays, which also producelarge amounts of ions because of their high kinetic energy. Suitableγ-ray sources are radioactive substances such as Cobalt 60 and Cesium137.

When negative ions are generated by the above method using discharge orirradiation, especially X-ray irradiation, ozone (O₃) may also begenerated. This ozone must be removed from the gas because it promotesoxidation of substrate surfaces. For the purpose of the presentinvention, the ozone concentration in a gas should desirably be 0.1 ppmor less, preferably 0.01 ppm or less, more preferably 1 ppb or less.Thus, it is preferable e.g. to use an inert gas free from the ozonesource O₂ such as N₂ or to subject the product negative ion-enriched gasto an ozone removal treatment in the discharge- or irradiation-basedmethod. Humidification of the gas after generation of negative ions maybe preferred for some purposes or desired specifications becausehumidification promotes decomposition of ozone.

A means for removing generated ozone from the negative ion-enriched gasis to treat the gas with a well-known O₃-treating agent after negativeions have been generated. Well-known O₃-treating agents that can be usedfor this purpose include e.g. Mn-based catalysts. The materials andforms of O₃-treating agents that can be used in the present inventionshould preferably consume little negative ions generated and coexistingin the gas, e.g. manganese dioxide-based honeycomb or mesh catalystssuch as MnO₂/TiO₂—C and MnO₂/ZrO—C.

Characteristics of each of the negative ion generating methods describedabove are shown in Table 1 below, wherein various methods are relativelyevaluated as follows: ∘ means good and Δ means slightly poor. TABLE 1Characteristics of various negative ion generating methods Amount/Large- Small- concen- Antioxidant scale scale tration of effect/ appli-appli- negative ions purity of cability cability generated negative ionsSafety Photoelectron Δ Δ-◯ Δ ◯ ◯ Discharge ◯ ◯ ◯ Δ-◯ ◯ Water spray ◯ Δ ◯Δ-◯ ◯ Irradiation ◯ ◯ ◯ Δ-◯ Δ

As shown from the table above, the photoelectron-based method is poor inlarge-scale applicability but good in antioxidant effect becauseozone-free clean negative ions are generated, while theirradiation-based method is good in large-scale and small-scaleapplicabilities and the amount of negative ions generated butinsufficient in safety. In the present invention, desirable negative iongenerating methods can be appropriately selected depending on thepurpose and desired performance or other factors, taking into accountadvantages and disadvantages of various negative ion generating methodsdescribed above.

It was found that when negative ions generated by the discharge-basedmethod were then humidified or they are generated by the waterspray-based method, the resulting negative ions had larger particlediameters than obtained by the others negative ion generating methodsdescribed above. For example, negative ions formed by thephotoelectron-based method or the discharge-based method withouthumidification have a particle diameter of about 1 nm, but negative ionsformed by the discharge-based method followed by humidification orgenerated by the water spray-based method have a particle diameter ofabout 3-5 nm. Our studies revealed that negative ions of larger particlediameters are more effective for inhibiting oxidation of substratesaccording to the present invention. The detailed reason for this isunknown, but supposed as follows. Negative ions consist of a negativelycharged core molecule (e.g. oxygen molecule) to which water moleculesare adsorbed (attached), and a somewhat large number of the watermolecules adsorbed are more effective for inhibiting oxidation ofsubstrates. Thus, the negative ion generating method using dischargefollowed by humidification or using water spray is preferably used forsome purposes, scales of equipments and desired specifications.

When a substrate is treated in the presence of thus prepared negativeion-enriched gas in the present invention, it is more effective forinhibiting oxidation of the substrate if a positive electrode is placedin the direction of the site where the negative ion-enriched gas isapplied, i.e. the substrate-processing site to attract negative ions inan electric field. This is because negative ions slowly move so thatthey are much consumed with some shapes or structures of equipments.

Negative ions generated to form a negative ion-enriched gas in thepresent invention as described above may be consumed by contaminants ifthey are contained in the gas. If micropartioulate substances exist inthe gas for example, the charges of generated negative ions aretransferred to these microparticles to form charged particles so thatthe negative ions are consumed. This lowers the concentration ofnegative ions to be effectively used for inhibiting oxidation ofsubstrates. It is known that semiconductor substrates are significantlycontaminated by the presence of microparticles and chemicalcontaminants, which results in a significant decrease in yield. Whennegative ions are generated in a gas containing acidic gases such asCl₂, negative ions having Cl₂ as a core are also formed and suchnegative ions do not suit the purpose of the present invention, i.e.“inhibiting oxidation of substrates” because they are thought to beoxidative. Therefore, it is desirable to sufficiently eliminate suchchemical contaminants before entering into the negative ion generatingstage.

From this point of view, a gas preliminarily freed of microparticles andchemical contaminants such as ionic components and inorganic and organicmatters are preferably passed through the negative ton generatordescribed above to generate negative ions in the present invention.Specifically, the gas supplied to the negative ion generator in thepresent invention preferably has a microparticle concentration of class(the number of particles having a standard particle diameter of 0.1 μmin 1 ft³ of a gas) 100 or less, preferably 10 or less, more preferably 1or less; an ionic component concentration of 10 μg/m³ or less,preferably 5 μg/m³ or less, more preferably 2 μg/m³ or less; and anorganic matter concentration of 10 μg/m³ or less, preferably 5 μg/m³ orless, more preferably 2 μg/m³ or less. The “ionic components” here referto acidic gases such as NO_(x), SO_(x), HCl, HF, Cl₂, F₂, HBr and Br₂;and basic gases such as ammonia and amine.

As described above, the gas supplied to the negative ion generatorshould preferably have preliminarily undergone contaminant removaltreatments. The contaminant removal treatments that can be performedbefore generating negative ions in the present invention are mainlyclassified into removal of microparticles and removal of chemicalcontaminants specifically explained below.

B. Removal of Microparticles

The gas to be treated to generate negative ions in the present inventionshould preferably be preliminarily freed of microparticles to class 100or less, preferably 10 or less, more preferably 1 or less, and anymicroparticle removing means known in the art can be used so far as thiscleanliness can be achieved. Microparticle removing means that can beused in the present invention include e.g. the use of a filter orphotoelectrons as proposed by us elsewhere.

B-1: Microparticle Removing Means Using Filters

Filters that can be used as microparticle removing means in the presentinvention include those well-known in the art such as ULPA filters, HEPAfilters, medium performance filters and electrostatic filters, which canbe used alone or combined.

B-2: Microparticle Removing Means Using Photoelectrons

This means removes microparticles using photoelectrons proposed by us inJP-B-HEI-6-74909, JP-B-HEI-7-121369, JP-B-HEI-8-211, JP-B-HEI-8-22393,Japanese Patent No. 2623290, etc. This method involves generatingnegative ions in the same manner as described above for the negative iongenerating method using photoelectrons, charging microparticles with thenegative ions generated and collecting/removing the chargedmicroparticles using an electrode or the like. Thus, thephotoelectron-based microparticle removing means that can be used in thepresent invention comprises a photoelectron emitting member, a UVsource, an electrode member and a charged microparticle collectingmember. The photoelectron emitting member, UV source and electrodemember can be those described above for the negative ton generatingmethod using photoelectrons.

Suitable charged microparticle collecting members typically includevarious electrode members such as dust collecting plates and dustcollecting electrodes or electrostatic filters used in conventionalparticle charging devices, but wool structures such as steel woolelectrodes and tungsten wool electrodes can also be effectively used.Electret members can also be suitably used.

Preferred combinations of the photoelectron emitting member, electrodemember and charged microparticle collecting member can be appropriatelyselected depending on the shape and structure of the space to becleaned, desired performance and economical efficiency. For example, thelocations and shapes of the photoelectron emitting member and electrodecan be appropriately determined taking into account the shape of thespace, effect, economical efficiency and other factors in such a mannerthat they can surround a UV source to combine the UV source,photoelectron emitting member, electrode member and chargedmicroparticle collecting member into a unit, which can effectively useUV rays emitted from the UV source and efficiently emit photoelectronsand charge/collect microparticle by the photoelectrons. When a rod-likeor cylindrical UV lamp is used as a UV source, for example, UV rays areradially emitted around the circumference of the lamp and the amount ofphotoelectrons emitted increases by irradiating the photoelectronemitting member with the circumferential radial UV rays as much aspossible. Thus, it is preferred that the photoelectron emitting memberis circumferentially located opposite the UV lamp and the photoelectronemitting electrode is located on the opposed face.

C. Removal of Ionic Components and Chemical Contaminants

As described above, the gas to be treated to generate negative ions inthe present invention should preferably be preliminarily freed of ioniccomponents such as acidic gases including Cl₂, NO_(x) and SO_(x) andbasic gases including ammonia; and chemical contaminants such asinorganic and organic matters, specifically to an ionic componentconcentration of 10 μg/m³ or less, preferably 5 μg/m³ or less, morepreferably 2 μg/m³ or less; and an organic matter concentration of 10μg/m³ or less, preferably 5 μg/m³ or less, more preferably 2 μg/m² orless. Suitable means for removing such contaminants can be any methodswell-known in the art, e.g. using adsorbents or photocatalysts, asspecifically explained below.

C-1: Means for Removing Chemical Contaminants Using Adsorbents

In the present invention, the means for removing chemical contaminantsusing adsorbents consists in collecting/removing acidic gases such asNO_(x), SO_(x), HCl, HF, Cl₂, F₂, HBr and Br₂; and basic gases such asammonia and amine in a gas to be treated during generation of a negativeion-enriched gas, and any adsorbents can be used so far as theyefficiently adsorb various acidic/basic gases mentioned above to lowconcentrations. Such known adsorbents include silica gel, zeolite,alumina, activated carbon and ion exchange fibers, among which activatedcarbon and ion exchange fibers are effective and therefore can bepreferably used in the present invention. Especially, ion exchangefibers can be preferably used for some purposes because they can collectcontaminants to low concentrations via chemical reactions and highcleanliness can be achieved. Activated carbon can be appropriately usedas those impregnated with an acid or alkali depending on the componentto be collected.

The adsorbents described above can be used in any shape, but generallyfibrous and honeycomb shapes are preferred because of small pressureloss.

Ion exchange fibers comprise a cation exchanger or an anion exchanger oran ion exchanger having both cation and anion exchange groups supportedon the surface of a carrier such as a natural or synthetic fiber or amixture thereof, and the ion exchanger may be directly supported on afibrous carrier or the ion exchanger may be supported on a woven orknitted or flocked base formed of fibers. Ion exchange fibers that canbe used in the present invention are preferably those prepared by graftpolymerization, especially radiation-induced graft polymerization. Thisis because radiation-induced graft polymerization allows ion exchangefibers to be formed using various types and shapes of materials.

The natural fibers can be wool, silk and the like, and the syntheticfibers can be those derived from hydrocarbon polymers orfluorine-containing polymers or polyvinyl alcohol, polyamide, polyester,polyacrylonitrile, cellulose or cellulose acetate. The hydrocarbonpolymers include aliphatic polymers such as polyethylene, polypropylene,polyisobutylene and polybutene; aromatic polymers such as polystyreneand poly α-methylstyrene; alicyclic polymers such as polyvinylcyclohexane; or copolymers thereof. The fluorine-containing polymersinclude polyethylene tetrafluoride, polyvinylidene fluoride,ethylene-ethylene tetrafluoride copolymers, ethylenetetrafluoride-propylene hexafluoride copolymers, vinylidenefluoride-propylene hexafluoride copolymers, etc. Any of these materialsare preferred as carriers for ion exchanges so far as they have a largearea in contact with gas stream, a shape with low resistance for easygrafting and a high mechanical strength with less waste fibers droppingand produced, and are less susceptible to heat, and they can beappropriately selected by those skilled in the art taking into accountthe intended use, economical efficiency, effect and other factors, butnormally polyethylene or composite materials of polyethylene andpolypropylene are preferably used.

Ion exchangers that can be introduced into these materials are notspecifically limited, but include various cation exchangers or anionexchangers. For example, suitable ion exchangers contain cation exchangegroups such as carboxyl, sulfonate, phosphate and phenolic hydroxyl; oranion exchange groups such as primary to tertiary amino groups andquaternary ammonium group; or both of the cation and anion exchangegroups mentioned above. Specifically, fibrous ion exchangers having acation exchange group or an anion exchange group can be obtained bygraft-polymerizing e.g. acrylic acid, methacrylic acid, vinyl benzenesulfonic acid, a styrene compound such as styrene, halomethylstyrene,acyloxystyrene, hydroxystyrene or aminostyrene; vinyl pyridine,2-methyl-5-vinyl pyridine, 2-methyl-5-vinylimidazole or acrylonitrileonto the fibrous base described above optionally followed by reactionwith sulfuric acid, chlorosulfonic acid or sulfonic acid. Alternatively,the above monomers may be graft-polymerized onto the fiber in thepresence of a monomer having two or more double bonds such asdivinylbenzene, trivinylbenzene, butadiene, ethylene glycol, divinylether or ethylene glycol dimethacrylate.

The diameter of the ion exchange fiber preferred for use as a chemicalcontaminant adsorbent in the present invention is 1-1000 μm, preferably5-200 μm and can be appropriately determined depending on the type ofthe fiber, purpose, etc. The type and amount of the cation exchangegroup and anion exchange group introduced into the ion exchange fibercan be determined depending on the type and concentration of thecomponent to be removed in the gas to be treated. For example, the typeand amount of the ion exchange group can be determined on the basis ofpreliminary measurement/evaluation of the component to be removed in agas. For example, fibers having a cation exchange group or an anionexchange group or both cation and anion exchange groups can be useddepending on whether the gas to be removed is basic or acidic or amixture of both.

The gas is effectively supplied to the ion exchange fiber at right angleto the ion exchange fiber in the form of a filter. The flow rate of thegas supplied to the ion exchange fiber can be appropriately determinedby pretests, but the gas can be normally supplied at about 1,000-100,000(h⁻¹) expressed as SV (spatial velocity) in view of the high removalrate of ion exchange fibers for gaseous components. Ion exchange fibersprepared by radiation-induced graft polymerization as previouslyproposed by us can be preferably used as appropriate because they areespecially effective (JP-B-HEI-5-9123, JP-B-HEI-5-67235,JP-B-HEI-5-43422, JP-B-HEI-6-24626, etc.). When ion exchange groups areintroduced into fiber materials (carriers) by radiation-induced graftpolymerization, the ion exchange capacity increases because the carriersare homogeneously irradiated to depth so that ion exchangers are firmlyfixed at high density over a large area. As a result, even lowconcentrations of gaseous components can be rapidly and efficientlyremoved. The preparation of ion exchange fibers by radiation-inducedgraft polymerization also has the following advantages. The preparationcan be performed with a material having a shape close to that of thetarget product at room temperature in a gas phase with high graftingdegree to give an adsorption filter containing low levels of impurities.Thus, ion exchange fibers prepared by radiation-induced graftpolymerization rapidly adsorb much gaseous components because ionexchangers having the function of adsorbing gaseous components arehomogeneously fixed in large quantity at high density. Moreover, filtermaterials with small pressure loss can be formed.

For some specifications desired, adsorbents formed from glass andfluorine resins such as a glass fiber filter having a fluorine resin asa binder can also be preferably used as chemical contaminant removingadsorbents in the present invention. Such filters are effective forremoving gaseous organic matters and particulate materials at the sametime (Japanese Patent No. 2582806).

C-2: Means for Removing Chemical Contaminants Using Photocatalysts

Means for removing chemical contaminants in a gas using photocatalystsare preferred when gaseous components to be removed contain organicmatters (HCs) such as phthalate esters. High molecular weight HCsincluding phthalate esters such as DOP must be removed because theycause lowered productivity and yield such as deteriorated pressureresistance of oxide films and lowered reliability once they are adsorbedto substrate surfaces.

Any photocatalysts can be used so far as they can be exited byirradiation to decompose HCs into inert forms for substrates such as CO₂and H₂O. Normally, semiconductor materials are preferably used asphotocatalysts in the present invention because they are effective andreadily available with good workability. In view of the effect andeconomical efficiency, any one of Se, Ge, Si, Ti, Zn, Cu, Al, Sn, Ga,In, P, As, Sb, C, Cd, S, Te, Ni, Fe, Co, Ag, Mo, Sr, W, Cr, Ba and Pb orcompounds or alloys or oxides thereof are preferred and can be usedalone or in combination of two or more.

Examples are elements such as Si, Ge and Se; compounds such as AlP,AlAg, GaP, AlSb, GaAs, InP, GaSb, InAs, InSb, CdS, CdSe, ZnS, MoS₂,WTe₂, Cr₂Te₃, MoTe, Cu₂S, and WS₂; and oxides such as TiO₂, Bi₂O₃, CuO,Cu₂O, ZnO, MoO₃, InO₃, Ag₂O, PbO, SrTiO₃, BaTio₃, Co₃O₄, Fe₂O₃ and NiO.For some applications, a metal member can be baked to form aphotocatalyst on the surface of the metal member. For example, aphotocatalyst can be prepared by baking a Ti member at 1000° C. to formTiO₂ on its surface (JP-A-HEI-11-90236). The above photocatalystmaterials are preferably used with additives such as Pt, Ag, Pd, RuO₂and Co₃O₄ to promote the HC-decomposing effect of the photocatalysts.These additives can be used alone or in combination. The dose isnormally 0.01-10% by weight relative to the photocatalyst and optimalconcentrations can be appropriately selected by preliminary experimentsdepending on the type of the additive and desired performance or thelike. Additives can be added by well-known techniques such as immersion,photoreduction, sputter deposition and kneading.

The photocatalysts can be used by immobilizing them in a space where thegas to be treated circulates or on the wall face of a channel throughwhich the gas flows or suspending them in a space where the gascirculates. The photocatalysts can be immobilized in a unit by coatingthe photocatalysts on an appropriate material in the form of a plate,flocculent, line, fiber, mesh, honeycomb, membrane, sheet or fabric orwrapping or inserting them in or between these materials. For example,any one of photocatalyst materials can be immobilized on a ceramic,metal, fluorine resin or glass material by appropriately using awell-known fixing means such as sol-gel process, sintering, vapordeposition or sputtering. Preferred materials on which photocatalystsare immobilized are normally in the form of a fiber, mesh or honeycombbecause of the small pressure loss. For example, TiO₂ fixed on a glassfiber by sol-gel process or a photocatalyst fixed on the surface of atransparent linear article (JP-A-HEI-7-256089) can be used as a meansfor removing chemical contaminants in a gas in the present invention.

In the present invention, the light source for irradiatingphotocatalysts can be any one of well-known light sources that canirradiate the photocatalysts to produce a photocatalytic effect. Thus,photocatalytic decomposition of HCs can be accomplished by bringing agas to be treated with a photocatalyst while irradiating thephotocatalyst with light beams having an absorbance wavelength rangedetermined by the type of the photocatalyst.

Main absorbance wavelength ranges of various photocatalysts are asfollows. Si:<1,100(nm); Ge:<1,825(nm): Se:<590(nm); AlAs:<517(nm);AlSb:<827(nm); GaAs:<886(nm); InP:<992(nm); InSb:<6,888(nm);InAs:<3,757(nm); CdS:<520(nm); CdSe:<730(nm); MoS₂:<585(nm);ZnS:<335(nm); TiO₂:<415(nm); Zno:<400(nm); Cu₂O:<625(nm); PbO:<540(nm);Bi₂O₃:<390(nm).

The light source used for irradiating the photocatalysts can beappropriately selected from any well-known light sources having awavelength in the absorbance range of the photocatalysts such assunlight and UV lamps. Suitable UV sources normally include mercurylamps, hydrogen discharge tubes, xenon discharge tubes and Lymandischarge tubes and they can be appropriately used. Specific forms ofsuitable light sources include germicidal lamps, black light lamps,fluorescent chemical lamps, UVB lamps and xenon lamps. Among them,germicidal lamps (main wavelength 254 nm) can be especially preferablyused for the following reasons. They can increase the effectiveirradiation dose to photocatalysts to increase photocatalytic effect;they are free from ozone; they can be easily installed; they areinexpensive and easy to maintain and manage; and they have highperformance. The irradiation dose to photocatalysts is generally0.05-50-mW/cm², preferably 0.1-10-mW/cm².

HCs can also be collected by using adsorbents such as activated carbon,but the use of adsorbents has problems with adsorption capacity andbreakthrough. That is, the adsorption capacity becomes rapidly saturatedat high concentrations of the gas generated, which requires additionaloperations such as replacement, while breakthrough invites the problemof secondary pollution due to the spill of collected matters. Incontrast, photocatalysts can be very preferably used as means forremoving chemical contaminants such as HCs in the present inventionbecause they are free from accumulation of HCs and can stably decomposeHCs for a long period.

Next, the water content that is important for generating negative ionsin the present invention is explained.

Water in a gas plays an important role in the mechanism by whichnegative ions are generated in the present invention. Thus, negativeions that are effective for inhibiting oxidation of substrates can beefficiently obtained by controlling the water content in the gas.

Especially, the mechanism by which negative ions are generated using thephotoelectron-based method and the discharge-based method is thought tobe explained as follows. Electrons generated may form negative ionclusters such as O₂ ⁻(H₂O)_(n), O⁻(H₂O)_(n) and OH⁻(H₂O)_(n) by theelectron attachment or clustering to molecules having high electronaffinity such as water molecules and oxygen molecules. These reactionsare shown below. $\begin{matrix}{{O_{2} + e^{-}}->O_{2}^{-}} \\{{O_{2}^{-} + {H_{2}O}}->{O_{2}^{-}\left( {H_{2}O} \right)}} \\\vdots \\{{{O_{2}^{-}\left( {H_{2}O} \right)}_{n - 1} + {H_{2}O}}->{O_{2}^{-}\left( {H_{2}O} \right)}_{n}}\end{matrix}$

As shown from the formulae above, water charged with electrons becomesnegative ions. Thus, it is not necessary to control the water contentwhen electrons are supplied to correspond to the water content in thegas. If the concentration of generated electrons is low, however, waterhaving the so-called oxidative effect harmful to wafers is liberated toadversely affect the wafers. The presence of such harmful water can beknown by testing the oxidation state of the wafer surface exposed to theatmosphere, e.g. the state of formation of natural oxide films. If thepresence of harmful water is detected in this manner, dehumidificationto an appropriate content is preferred. For the purpose of removingharmful water, dehumidification is preferred to a relative humidity in agas of about 45±5%, preferably 30% or less, more preferably 20% or less.Dehumidification of the gas can be accomplished by appropriately using awell-known method preferably before negative ions are generated normallyin the present invention.

Dehumidifying means that can be used in the present invention includewell-known methods such as cooling, adsorption, absorption, compressionand membrane separation, and one or more of the above means can be usedin combination after appropriate pretests depending on the field towhich the present invention is to be applied and the scale,configuration and operation conditions of the equipments, e.g. whetherit is applied under atmospheric or pressurized condition. Thedehumidifying means preferably keeps stable dehumidification performanceover a long period, normally several to six months or longer, andespecially the means based on cooling, adsorption or membrane separationare simple and effective. Preferred dehumidifying means based on coolingare electronic dehumidification and cooling coils because of the compactstructure and effectiveness and preferred dehumidifying means based onadsorption are systems in which the dehumidifier per se is regeneratedfor continuous long dehumidification (fixed or rotary system) because ofthe simplicity and effectiveness. Dehumidifying materials that can beused in the adsorption-based dehumidifying means include silica gel,zeolite, activated carbon, activated alumina, magnesium perchlorate,calcium chloride, alumina-pillared clay porous materials, boundactivated carbon and porous aluminum phosphate. The alumina pillaredclay porous materials here refer to materials obtained by exchangingexchangeable cations between layers of a layered silicate withmultinuclear metal hydroxide ions including aluminum and dehydrating theion exchanged silicate by heating. The bound activated carbon isobtained by carbonizing polyvinyl formal and activating it at atemperature of 850° C. or less. Porous aluminum phosphate is also calledmolecular sieve and obtained by reacting an alumina hydrate such asaluminum hydroxide, boehmite or pseudoboehmite with phosphoric acidusing a heat-dissociable template such as an organic base, e.g.tripropylamine.

In the negative ton generating method using water spray, it is necessaryto remove harmful water using well-known dehumidifying means such aseliminators or heating coils because the so-called water mist isgenerated by water spray (atomization).

Dehumidification described above is applied when the amount of electronsin a gas is 0.1 PA or less expressed as the current value measured in aspace, but reversely the gas is preferably humidified to generatenegative ions to which more water molecules are attached when this valueis 0.1 PA or more. Humidification can be accomplished by meanswell-known In the art, e.g. by heating water with a heater or vaporizingor ultrasonically spraying or supplying water through a membrane. Whenwater is added to the gas by humidification, excess water not havingparticipated in generating negative ions is preferably removed by usinga dehumidifying means such as an eliminator or heating coil.

As described above, effective negative ion-enriched gases for inhibitingoxidation at proper water contents can be formed by appropriately usinghumidifying means and dehumidifying means. Thus, a proper amount ofwater can be effectively used as a negative ion source by properlycontrolling water contents.

Inert gases such as N₂ and Ar can be used as gases for generatingnegative ions to form a negative ion-enriched gas and such inert gasesare preferably hydrated by the humidifying means described above becausethey are normally dry and cannot efficiently generate negative ions assuch. The amount of water to be added can be determined afterappropriate pretests depending on the negative ion generating method,desired specification and other factors.

Next, several specific embodiments of semiconductor manufacturingequipments according to the present invention are explained withreference to the attached drawings.

FIG. 1 shows specific processing steps on a semiconductor substrate in asemiconductor factory (clean room, class 10,000). The present inventioncan be applied to each specific processing step shown in FIG. 1. Thatis, a semiconductor manufacturing equipment of the present inventioncomprises a negative ion-enriched gas generator as explained below and ameans for supplying the negative ion-enriched gas prepared by saidgenerator to the surface of a substrate in a semiconductor processingequipment at various specific processing steps shown in FIG. 1. Forexample, a substrate can be cleaned/dried while inhibiting oxidation ofthe substrate by combining an apparatus comprising a “negativeion-enriched gas generator” and a “means for supplying the resultingnegative ion-enriched gas to the surface of a substrate” explained belowwith an “apparatus for spraying a gas to a substrate to wash and dry thesurface of the substrate with air”, which can be used during the step“clean and dry the substrate” shown in FIG. 1.

FIG. 2 shows a schematic view of a negative ion-enriched gas generatoraccording to an embodiment of the present invention comprising a cleangas generator consisting of an adsorbent-based chemical contaminantremoving means and a filter-based microparticle removing means; and adischarge-based negative ion generator. Such an apparatus generates anegative ion-enriched air at class 10 or less free from chemicalcontaminants (100,000 negative ions/mL or more). Semiconductorsubstrates can be prevented from contamination by performing eachspecific processing step shown in FIG. 1 while exposing the surfaces ofthe semiconductor substrate to the negative ion-enriched air generatedin the present example.

Negative ion-enriched air generator A shown in FIG. 2 comprises a fan 20for supplying a clean room air, an adsorbent (ion exchange fiber andactivated carbon) 21 for removing chemical contaminants in the cleanroom air, a dust filter (ULPA filter) 22 for removing microparticles inthe clean room air (class 10,000) and microparticles. generated from fan20, a discharging member (corona discharge) 23 for generating negativeions, and an O₃ decomposing/removing member 24 for removing O₃ generatedfrom discharging member 23. In the figure, 25-1 indicates the flow ofthe air introduced by fan 20 into negative ion-enriched gas generator A,25-2 indicates the flow of the negative ion-enriched gas generated bynegative ion-enriched gas generator A, and 26 represents negative ions.In discharging member 23 In FIG. 2, 23-1 represents a needle-likedischarge electrode and 23-2 represents a counter electrode.

According to negative ion-enriched gas generator A shown in FIG. 2. aclean room air (having a microparticle concentration of class 10,000 anda negative ion concentration of 100 ions/mL or less) introduced by thefan first passes through adsorbent 21 for collecting chemicalcontaminants and filter 22 for collecting microparticles, whereby it iscleaned to a microparticle concentration of class 10 or less and bothionic component concentration and organic matter concentration of 2μg/m³ or less. Then, negative ions are generated by discharge-basednegative ion generator 23, and generated ozone is removed by ozonedecomposing/removing member 24, whereby a clean negative ion-enrichedgas is provided having a concentration of 100,000 negative ions/mL ormore, a microparticle concentration of class 10 or less, both ioniccomponent concentration and organic matter concentration of 2 μg/m³ orless, and an ozone concentration of 0.01 ppm or less. This negativeion-enriched gas can be used as a substrate-exposing gas in variousprocessing steps shown in FIG. 1 to achieve a semiconductormanufacturing process in which substrates are inhibited from oxidationand both microparticle contamination and chemical contamination areprevented.

FIG. 3 shows a schematic view of a negative ion-enriched gas generatoraccording to another embodiment of the present invention, comprising aclean gas generator using adsorbent/microparticle collecting filter anda photoelectron-based negative ion generator. In FIG. 3, similarelements to those shown in FIG. 2 are designated with the samereferences and not explained.

Negative ion-enriched air generator A shown in FIG. 3 comprises acleaner consisting of a chemical contaminant-collecting adsorbent 21 anda microparticle-collecting filter 22; and a negative ion generatorconsisting of a photoelectron emitting member 27, a UV lamp 28 and anelectric field-forming electrode 29. According to negative ion-enrichedgas generator A shown in FIG. 3, a clean room air introduced by the fanis cleaned through chemical contaminant-collecting adsorbent 21 andmicroparticle-collecting filter 22 to a microparticle concentration ofclass 10 or less and both ionic component concentration and organicmatter concentration of 2 μg/m³ or less, then introduced into thenegative ion generator where photoelectron emitting member 27 isirradiated with UV rays to emit photoelectrons. Thus, a clean negativeion-enriched gas is provided having a concentration of 10,000 negativeions/mL or more, a microparticle concentration of class 10 or less, andboth ionic component concentration and organic matter concentration of 2μg/m³ or less. According to the photoelectron-based method, the ozoneremoving member as shown in FIG. 2 is normally unnecessary because ozoneis not generated. The negative ion-enriched gas generated by negativeion-enriched gas generator A shown in FIG. 3 can be used as asubstrate-exposing gas in various processing steps shown in FIG. 1 toachieve a semiconductor manufacturing process In which substrates areinhibited from oxidation and both microparticle contamination andchemical contamination are prevented.

FIG. 4 shows a schematic view of a negative ion-enriched gas generatoraccording to another embodiment of the present invention, comprising aclean gas generator consisting of an adsorbent-based chemicalcontaminant-removing means and a microparticle-removing means; and aphotoelectron-based negative ion generator as shown in FIG. 3. In FIG.4, similar elements to those shown in FIG. 3 are designated with thesame references.

Negative ion-enriched air generator A shown in FIG. 4 comprises a cleangas generator consisting of a chemical contaminant-collecting adsorbent21 and a microparticle removing means formed of a photoelectron emittingmember 41, a UV lamp 42, an electric field-forming electrode 43 and acharged microparticle collecting member 44; and a negative ion generatorconsisting of a photoelectron emitting member 27, a UV lamp 28 and anelectric field-forming electrode 29. According to negative ion-enrichedgas generator A shown in FIG. 4, a clean room air introduced by the fanfirst passes through chemical contaminant-collecting adsorbent 21 wherechemical contaminants in the gas are removed. Then, the gas isintroduced into the photoelectron-based microparticle removing meanswhere photoelectron emitting member 41 is irradiated with UV rays toemit photoelectrons, which generate negative ions. Then, microparticlesin the gas are charged with the negative ions generated. The chargedmicroparticles are collected/removed by charged microparticle collectingmember 44 at the subsequent stage. As a result, a gas cleaned to amicroparticle concentration of class 100 or less and both ioniccomponent concentration and organic matter concentration of 2 μg/m³ orless is formed, and this clean gas is introduced into the negative iongenerator, where photoelectron emitting member 27 is irradiated with UVrays to emit photoelectrons. Thus, a clean negative ion-enriched gas isprovided having a concentration of 5,000 negative ions/mL or more, amicroparticle concentration of class 100 or less, and both ioniccomponent concentration and organic matter concentration of 2 μg/m³ orless. The negative ion-enriched gas generated by negative ion-enrichedgas generator A shown in FIG. 4 can be used as a substrate-exposing gasin various processing steps shown in FIG. 1 to achieve a semiconductormanufacturing process in which substrates are inhibited from oxidationand both microparticle contamination and chemical contamination areprevented.

FIG. 5 shows a schematic view of a negative ion-enriched gas generatoraccording to another embodiment of the present invention, comprising aclean gas generator using adsorbent/microparticle-collecting filter, anda negative ion generator using water spray. In FIG. 5, similar elementsto those shown in FIG. 2 are designated with the same references and notexplained.

Negative ion-enriched air generator A shown in FIG. 5 comprises acleaner consisting of a chemical contaminant-collecting adsorbent 21 anda microparticle-collecting filter 22; and a negative ion generatorconsisting of a water-spray nozzle 33, an excess water eliminator 34 anda water supply tank 31. According to negative ion-enriched gas generatorA shown in FIG. 5, a clean room air introduced by the fan is cleanedthrough chemical contaminant-collecting adsorbent 21 andmicroparticle-collecting filter 22 to a microparticle concentration ofclass 10 or less and both ionic component concentration and organicmatter concentration of 2 μg/m³ or less, then introduced into thenegative ion generator where water from water supply tank 31 is sprayedat a high pressure from water spray nozzle 33 through heat exchanger 32to form negative ions. The resulting negative ion-enriched gas is freedof excess water by eliminator 34 and heated to a desired temperature bya reheater 35. Thus, a clean negative ion-enriched gas is providedhaving a concentration of 200,000-300,000 negative ions/mL or more, amicroparticle concentration of class 10 or less, and both ioniccomponent concentration and organic matter concentration of 2 μg/m³ orless. Excess water collected by eliminator 34 is received in watersupply tank 31 and recycled to water spray nozzle 33. As describedabove, the ozone removing member as shown in FIG. 2 is normallyunnecessary because ozone is not generated according to thephotoelectron-based method. The negative ion-enriched gas generated bynegative ion-enriched gas generator A shown in FIG. 5 can be used as asubstrate-exposing gas in various processing steps shown in FIG. 1 toachieve a semiconductor manufacturing process in which substrates areinhibited from oxidation and both microparticle contamination andchemical contamination are prevented.

In the water spray-based negative ion generating method, about 10-20% ofpositive ions may be generated simultaneously with negative ions undersome conditions. Normally, any special means for removing positive ionsis not necessary because large amounts of negative ions are generatedand as low as 20% of positive ions are neutralized by negative ionsaccording to the water spray-based method if they are generated, but itmay be sometimes desirable to collect/remove positive ions by placing anegative electrode further downstream of reheater 35.

FIG. 6 shows a schematic view of a negative ion-enriched gas generatoraccording to another embodiment of the present invention, comprising aclean gas generator using adsorbent/microparticle-collecting filter anda negative ion generator using X-ray irradiation. In FIG. 6, similarelements to those shown in FIG. 2 are designated with the samereferences and not explained.

Negative ion-enriched air generator A shown in FIG. 6 comprises acleaner consisting of a chemical contaminant-collecting adsorbent 21 anda microparticle-collecting filter 22; and a negative ion generatorconsisting of a very weak X-ray (soft X-rays: wavelength 0.2-0.3 nm)generator 36. According to negative ion-enriched gas generator A shownin FIG. 6, a clean room air introduced by the fan is cleaned throughchemical contaminant-collecting adsorbent 21 andmicroparticle-collecting filter 22 to a microparticle concentration ofclass 10 or less and both ionic component concentration and organicmatter concentration of 2 μg/m³ or less, then introduced into thenegative ion generator where the gas is irradiated with X-rays so thatgas molecules are ionized to generate negative ions. In FIG. 6, Brepresents an ionization zone of gas molecules with X-rays. When the gasis irradiated with X-rays, negative ions and positive ions are generatedbut positive ions are removed by negative electrode 37. Thus, a cleannegative ion-enriched gas is provided having a concentration of 100,000negative ions/mL or more, a microparticle concentration of class 10 orless, and both ionic component concentration and organic matterconcentration of 2 μg/m³ or less. The negative ion-enriched gasgenerated by negative ion-enriched gas generator A shown in FIG. 6 canbe used as a substrate-exposing gas in various processing steps shown inFIG. 1 to achieve a semiconductor manufacturing process in whichsubstrates are inhibited from oxidation and both microparticlecontamination and chemical contamination are prevented.

During irradiation of the gas with X-rays to generate negative ions, aslight amount of ozone may be generated under some irradiationconditions. If there is a possibility that ozone is generated, an ozonedecomposing/removing member 24 is preferably placed further downstreamof negative electrode 37 for removing positive ions as shown in FIG. 7so that even a minor amount of ozone can be decomposed/removed if it isgenerated. Thus, a clean negative ion-enriched gas is provided having aconcentration of 100,000 negative ions/mL or more, a microparticleconcentration of class 10 or less, both ionic component concentrationand organic matter concentration of 2 μg/m³ or less, and an ozoneconcentration of 0.01 ppm or less, and this gas can be used as asubstrate-exposing gas in various processing steps shown in FIG. 1 toachieve a semiconductor manufacturing process in which substrates areinhibited from oxidation and both microparticle contamination andchemical contamination are prevented.

EXAMPLES

Negative ion-enriched gas generators according to various embodiments ofthe present invention shown in FIGS. 2 to 7 were used to preparenegative ion-enriched gases. The apparatuses used have the followingstructures.

1) Negative ion-enriched gas generator 1: the apparatus having thestructure shown in FIG. 2 (capacity: about 30 L)

-   -   Adsorbent 20: a mixed bed of an ion exchange fiber: activated        carbon (1:1);    -   Dust filter 21: ULPA filter;    -   Discharging member: 30 kV applied across the electrodes;    -   O₃ decomposing/removing member; MnO₂/TiO₂—C.

2) Negative ion-enriched gas generator 2: the apparatus having thestructure shown in FIG. 3 (capacity; about 30 L)

-   -   Adsorbent 20 and dust filter 21: the same as described above in        1):    -   UV lamp 28: a germicidal lamp (4 W);    -   Photoelectron emitting member 27: a thin film of Au coated on        TiO₂;    -   Electrode 29: a grid electrode made from SUS was placed above        the lamp as shown in FIG. 3: electric field 10 V/cm.

3) Negative ion-enriched gas generator 3: the apparatus having thestructure shown In FIG. 4 (capacity: about 40 L)

-   -   Adsorbent 20: the same as described above in 1);    -   Photoelectron emitting members 27 and 41, UV lamps 28 and 42,        electrodes 29 and 43; the same as described above in 2);    -   Charged microparticle collecting member: a Cu—Zn plate.

4) Negative ion-enriched gas generator 4: the apparatus having thestructure shown in FIG. 5 (capacity: about 200 L)

-   -   Adsorbent 20 and filter 21: the same as described above in 1):.    -   Water sprayer: atomization with water-spray nozzle 33 supplied        with 3 L/min of ion exchange water at a water pressure of 350        kPa and a water/air ratio (L/G)=1;    -   Reheater: produced water drops were vaporized using a reheating        coil.

5) Negative ion-enriched gas generator 5: the apparatus having thestructure shown in FIG. 6 (capacity: about 30 L)

-   -   Adsorbent 20 and filter 21: the same as described above in 1);    -   X-ray generator 36: wavelength 0.2-0.3 nm;    -   Negative electrode 37; a Ca—Zn plate.

Negative ion-enriched gas generators 1 to 3 and 5 described above weresupplied with a clean room air (microparticle concentration class10,000, organic matter concentration 100-120 μg/m³, NH₃ concentration15-20 μg/m³) at a flow rate of 3 L/min. Negative ion-enriched gasgenerator 4 described above was supplied with the same clean room air ata flow rate of 30 L/min. The properties of the air obtained fromnegative ion-enriched gas generators 1 to 5 are shown in Table 2 below.TABLE 2 Properties of negative ion-enriched gases Negative Negative ionMicro- Organic ion conc. particle matter Ammonia Cleaning generating(number/mL) conc. conc. conc. Apparatus method method Inlet Outletnumber/ft³ μg/m³ μg/m³ 1) FIG. 2 Adsorption/ Discharge ≦100 100,000≦ <10<2 <1 ULPA 2) FIG. 3 Adsorption/ Photoelectron ≦100  10,000≦ <10 <2 <1ULPA 3) FIG. 4 Adsorption/ Photoelectron ≦100  8,000-10,000 <100 <2 <1photoelectron 4) FIG. 5 Adsorption/ Water ≦100 200,000-300,000 <10 <1 <1ULPA spray 5) FIG. 6 Adsorption/ X-ray ≦100 100,000≦ <10 <1 <1 ULPAirradiation

The concentration of O₃ in the negative ion-enriched gas obtained byapparatus 1) was 0.01 ppm or less.

The surface of an Si wafer was exposed to the negative ion-enrichedgases obtained from negative ion-enriched gas generators 1 to 5described above and the production state of oxide films was observed. AnSi wafer high resolution XPS made by Scienta type ESCA300 was used asthe wafer sample after washed with RCA and then treated with HF (0.05%)and rinsed with pure water and dried, Negative ion-enriched gasesobtained from negative ion-enriched gas generators 1 to 5 above weresprayed on the surface of this wafer sample at a flow rate of 3 L/minand the thickness of the oxide film formed on the sample surface wasmeasured after given periods of time. The results are shown in Table 3below. As a comparative example, the surface of the same wafer samplewas exposed to the clean room air directly used. The results are alsoshown in Table 3 below. TABLE 3 Si wafer oxidation test Thickness ofoxide Ap- Negative ion film (angstroms) pa- Cleaning generating Afterexposure After exposure ratus method method for 3 hours for 12 hours 1)Adsorption/ Discharge <0.02 <0.02 ULPA 2) Adsorption/ Photoelectron<0.02 <0.02 ULPA 3) Adsorption/ Photoelectron <0.02 <0.02 photoelectron4) Adsorption/ Water spray <0.02 <0.02 ULPA 5) Adsorption/ X-ray <0.02<0.02 ULPA irradiation Comparative example: 0.3 5 exposed to clean roomair

Then, the wafer sample surface was exposed (exposure period: 12 h) togases containing about 500, about 1,000, about 3,000, about 5,000, about10,000, about 30,000 and about 50,000 negative ions/mL prepared undervarying treatment conditions using negative ion-enriched gas generator 1to determine effective negative ion concentrations for inhibiting theproduction of oxide films. An effect was shown at concentrations of1,000 negative ion s/mL or more as proved by oxide film thicknesses of<0.1 angstrom, and a remarkable effect was shown at 5,000 negativeions/mL or more as proved by <0.05 angstroms. An especially remarkableeffect was shown at 10,000 negative ions/mL or more as proved by <0.02angstroms.

Industrial Applicability

It was concluded from the foregoing findings that the present inventioncould have the following advantages.

(1) Substrates can be subjected to various processing steps whileinhibiting them from oxidation by supplying a negative ion-enriched gasinto the spaces of semiconductor manufacturing processes.

(2) Gases stable against pollution (having an antipollution function)can be prepared because clean negative ion-enriched gases free frommicroparticles and chemical components are obtained by removingmicroparticles and chemical contaminants.

(3) Generated negative ions can be prevented from being consumed bycontaminants such as microparticles by using a gas freed ofmicroparticles and chemical contaminants to prepare negativeion-enriched gases.

(4) It will be important in future to prevent substrate surfaces fromoxidation, in addition to current pollution sources such asmicroparticles and chemical contaminants. According to the presentinvention, clean gases can be obtained that also have an antioxidanteffect for substrate surfaces.

(5) More practical antipollution gases can be provided becausepreferable negative ion generating methods can be selected (see Table 1)depending on the preferred specifications such as the scale of theequipment to which the present invention is to be applied, the amount ofnegative ions to be generated and the desired antioxidant effect.

1-8. (canceled)
 9. A process for manufacturing a semiconductor,comprising: treating a substrate while exposing a surface of thesubstrate with a negative ion-enriched gas.
 10. The process of claim 9,wherein said negative ion-enriched gas is prepared by passing a cleangas freed of microparticles and/or chemical contaminant through anegative ion generator.
 11. The process of claim 10, wherein saidchemical contaminant is one or more selected from the group consistingof ionic components, inorganic matters, and organic matters.
 12. Theprocess of claim 10, wherein said negative ion-enriched gas is preparedby passing a gas having a microparticle concentration of class 100 orless, an ionic component concentration of 10 μg/m³ or less, and anorganic matter concentration of 10 μg/m³ or less through a negative iongenerator.
 13. The process of claim 9, wherein the concentration ofnegative ions in said negative ion-enriched gas is 1,000 negativeions/mL or more.
 14. The process of claim 9, wherein the concentrationof negative ions in said negative ion-enriched gas is 5,000 negativeions/mL or more.
 15. The process of claim 9, wherein the concentrationof negative ions in said negative ion-enriched gas is 10,000 negativeions/mL or more.
 16. The process of claim 9, wherein the concentrationof negative ions in said negative ion-enriched gas is 50,000 negativeions/mL or more.
 17. An equipment for manufacturing a semiconductorcomprising: a gas channel through which a gas to be treated is passed; anegative ion-enriched gas generator including a gas cleaner located atan upstream part of said gas channel and a negative ion generatorlocated at a downstream part of said gas channel; and means forsupplying resulting negative ion-enriched gas to a surface of asubstrate.
 18. The equipment of claim 17, wherein said gas cleanerprepares a gas having a microparticle concentration of class 100 orless, an ionic component concentration of 10 μg/m³ or less, and anorganic matter concentration of 10 μg/m³ or less.
 19. The equipment ofclaim 17, wherein said negative ion-enriched gas generator prepares anegative ion-enriched gas having a negative ion concentration of 1,000negative ions/mL or more.
 20. The process of claim 17, wherein theconcentration of negative ions in said negative ion-enriched gas is5,000 negative ions/mL or more.
 21. The process of claim 17, wherein theconcentration of negative ions in said negative ion-enriched gas is10,000 negative ions/mL or more.
 22. The process of claim 17, whereinthe concentration of negative ions in said negative ion-enriched gas is50,000 negative ions/mL or more.